Method of manufacturing semiconductor device that includes selectively adding a noble gas element

ABSTRACT

Phosphorus is implanted into a crystalline semiconductor film by an ion dope method. However, a concentration of phosphorus required for gettering is 1×10 20 /cm 3  or higher which hinders recrystallization by later anneal, and thus this becomes a problem. Also, when phosphorus is added at a high concentration, processing time required for doping is increased and throughput in a doping step is reduced, and thus this becomes a problem. The present invention is characterized in that impurity regions to which an element belonging to the group  18  of the periodic table is added are formed in a semiconductor film having a crystalline structure and gettering for segregating in the impurity regions a metal element contained in the semiconductor film is performed by heat treatment. Also, a one conductivity type impurity may be contained in the impurity regions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing asemiconductor device using a gettering technique and a semiconductordevice obtained by the manufacturing method. More particularly, thepresent invention relates to a method of manufacturing a semiconductordevice using a crystalline semiconductor film produced by adding a metalelement having catalysis to crystallization of a semiconductor film anda semiconductor device.

2. Description of the Related Art

A thin film transistor (hereinafter referred to as a TFT) is known as atypical semiconductor element using a semiconductor film having acrystalline structure (hereinafter referred to as a crystallinesemiconductor film). The TFT is noted as a technique for forming anintegrated circuit on an insulating substrate made of glass or the like,and a driver circuit integrated liquid crystal display device and thelike are putting into practical use. According to a conventionaltechnique, an amorphous semiconductor film deposited by a plasma CVDmethod or a low pressure CVD method is processed by heat treatment or alaser anneal method (technique for crystallizing a semiconductor film bylaser light irradiation) to produce the crystalline semiconductor film.

Since the crystalline semiconductor film thus produced is an aggregateof a large number of crystal grains, and its crystal orientation isoriented in an arbitrary direction which is thus uncontrollable, thiscauses a reduction in a characteristic of the TFT. To solve such aproblem, a technique disclosed in Japanese Patent Application Laid-openNo. Hei 7-183540 is one performed by adding a metal element havingcatalysis, such as nickel, in crystallization of an amorphoussemiconductor film, and orientation property of the crystal orientationcan be improved to be a single direction, in addition to an effect ofdecreasing a heating temperature required for the crystallization. Whena TFT is made from a crystalline semiconductor film produced by thismethod, a reduction in a subthreshold coefficient (S value) andimprovements of a static characteristic and a dynamic characteristicsbecome possible in addition to an improvement of electric field effectmobility.

However, since a metal element having catalysis is added, there is sucha problem that the metal element is left in the inner portion or thesurface of the crystalline semiconductor film, and thus a characteristicof an obtained TFT is varied. One example is increase of an off currentand there is such a problem that a variation between the individual TFTsis caused. That is, the metal element having catalysis tocrystallization conversely becomes unnecessary once the crystallinesemiconductor film has been formed.

Gettering using phosphorus is effectively used as a method of removingsuch a metal element from a specific region of the crystallinesemiconductor film. For example, phosphorus is added to a source and adrain regions of a TFT and then heat treatment is performed at 450 to700° C., whereby the metal element can be easily removed from thechannel forming region.

Phosphorus is implanted to the crystalline semiconductor film by an iondope method (which is a method of dissociating PH₃ or the like withplasma and accelerating ions of PH₃ by an electric field to implant itinto a semiconductor, and a method in which ion mass separation is notbasically performed). A concentration of phosphorus required forgettering is 1×10²⁰/cm³ or higher. Addition of phosphorus by the iondope method causes the crystalline semiconductor film to be amorphous.However, when the concentration of phosphorus is increased a problem inwhich recrystallization by later anneal is hindered is caused. Also,since the addition of high concentration phosphorus causes an increasein a processing time required for doping, a problem in which throughputin a doping process is decreased is caused.

Further, a concentration of boron required for inverting a conductivitytype is 1.5 to 3 times higher than that of phosphorus added to a sourceregion and a drain region of a p-channel TFT. Thus, a problem in whichresistances of the source region and the drain region are increasedaccording to difficulty of recrystallization is caused.

SUMMARY OF THE INVENTION

The present invention is a means for solving such problems, and anobject of the present invention is to provide a technique for easilyremoving a metal element left in a crystalline semiconductor filmobtained using the metal element having catalysis to crystallization ofan amorphous semiconductor film.

A gettering technique is positioned as a main technique in manufacturingtechniques of an integrated circuit using a single crystalline siliconwafer. The gettering is known as a technique in which a metal impuritytaken in a semiconductor is segregated in a gettering site by someenergy to reduce a concentration of the impurity present in an activeregion of an element. The gettering techniques are broadly divided intoextrinsic gettering and intrinsic gettering. The extrinsic getteringproduces a gettering effect by providing a chemical action or adistortion field from the outside. Gettering for diffusing phosphorushaving a high concentration from the rear surface of the singlecrystalline silicon wafer corresponds to this extrinsic gettering, andthe above gettering using phosphorus to the above-mentioned crystallinesemiconductor film can be assumed as a kind of extrinsic gettering. Onthe other hand, the intrinsic gettering is known as a techniqueutilizing a distortion field of lattice defect being related to oxygenproduced in the inner portion of the single crystalline silicon wafer.The present invention focuses on gettering utilizing the lattice defector the lattice distortion and which uses the following means forapplication to the crystalline semiconductor film with a thickness ofabout 10 to 100 nm.

The present invention is characterized in that an impurity region towhich a noble gas element belonging to the group 18 of the periodictable is added is formed in a semiconductor film having a crystallinestructure, and gettering for segregating in the impurity region a metalelement included in the semiconductor film by heat treatment isproduced. Also, a one conductivity type impurity, such as phosphorus orboron, may be contained in the impurity region.

A noble gas element preferably used in particular in the presentinvention is one kind or plural kinds of elements selected from thegroup consisting of He, Ne, Ar, Kr, and Xe. These ions are acceleratedby an electric field to be implanted into the semiconductor film,whereby dangling bond and lattice distortion are produced to make itpossible to form a gettering site. Also, an element belonging to thegroup 15 or group 13 of the periodic table is applied as a oneconductivity type impurity element and may be contained in the region towhich the noble gas element is added.

A method of manufacturing a crystalline semiconductor film, includinggettering processing using this noble gas element, comprises a firststep of adding a metal element to a semiconductor film having anamorphous structure; a second step of crystallizing the semiconductorfilm by first heat treatment to form a crystalline semiconductor film; athird step of forming in the crystalline semiconductor film an impurityregion to which a noble gas element is added; and a fourth step ofperforming gettering for segregating in the impurity region the metalelement included in the crystalline semiconductor film by a second heattreatment after the third step. In the third step, selective addition ofthe noble gas element can be performed by forming a mask insulating filmhaving an opening. Also, after the second heat treatment is completed,the impurity region to which the noble gas element is added is removedand a semiconductor region in which a concentration of the added metalelement is reduced can be formed as the crystalline semiconductor filmhaving a desired shape.

Also, a manufacturing method of the present invention includes: a firststep of selectively adding a metal element to a first region of asemiconductor film having an amorphous structure; a second step ofcrystallizing the semiconductor film by first heat treatment to form acrystalline semiconductor film; a third step of adding in the firstregion of the crystalline semiconductor film a noble gas element; and afourth step of performing gettering for segregating in the first regionthe metal element contained in the second semiconductor film by secondheat treatment after the third step. After the second heat treatment iscompleted, the impurity region to which the noble gas element is addedis removed and a semiconductor region in which a concentration of theadded metal element is reduced can be formed as the crystallinesemiconductor film having a desired shape.

Also, a method of manufacturing a crystalline semiconductor film bygettering using a noble gas element according to the present inventionis characterized in that an impurity region to which a noble gas element(also called a noble gas) is added is formed in a crystallinesemiconductor film and gettering for segregating in the impurity regiona metal element contained in the semiconductor film by heat treatment isperformed, and then the semiconductor film having the crystallinestructure is irradiated with intense light. The noble gas element is onekind or plural kinds of elements selected from the group consisting ofHe, Ne, Ar, K, and Xe. These ions are accelerated by an electric fieldto be implanted into the semiconductor film, whereby dangling bond andlattice distortion are produced to make it possible to form a getteringsite.

A one conductivity type impurity may be added to the impurity region towhich the noble gas element is added, and thus both the noble gaselement and the one conductivity type impurity are contained in theimpurity region. An element belonging to the group 15 or group 13 of theperiodic table is applied as the one conductivity type impurity. Inaddition, hydrogen may be added to the impurity region, and the noblegas element, the one conductivity type impurity, and hydrogen are allcontained in the impurity region.

An element belonging to the group 15 of the periodic table and anelement belonging to the group 13 thereof may be added to the impurityregion to which the noble gas element is added, and the noble gaselement, the element belonging to the group 15 of the periodic table andthe element belonging to the group 13 thereof are all included in theimpurity region.

An element belonging to the group 15 of the periodic table and anelement belonging to the group 13 thereof, and hydrogen may be added tothe impurity region to which the noble gas element is added, and thusthe noble gas element, the element belonging to the group 15 of theperiodic table, the element belonging to the group 13 thereof, andhydrogen are all contained in the impurity region.

Thus, a method of manufacturing a crystalline semiconductor film using anoble gas element comprises a first step of adding a metal element to afirst semiconductor film having an amorphous structure; a second step ofcrystallizing the first semiconductor film by first heat treatment toform a second semiconductor film having a crystalline structure; a thirdstep of forming an impurity region to which the noble gas element isadded in the second semiconductor film; a fourth step of performinggettering for segregating in the impurity region the metal elementcontained in the second semiconductor film by second heat treatmentafter the third step; and a fifth step of irradiating the semiconductorfilm having the crystalline structure with intense light.

Alternatively, a manufacturing method of the present inventioncomprises: a first step of adding a metal element to a firstsemiconductor film having an amorphous structure; a second step ofcrystallizing the first semiconductor film by first heat treatment toform a second semiconductor film having a crystalline structure; a thirdstep of forming an impurity region to which a one conductivity typeimpurity and a noble gas element are added in the second semiconductorfilm; a fourth step of performing gettering for segregating in theimpurity region the metal element contained in the second semiconductorfilm by second heat treatment after the third step; and a fifth step ofirradiating the semiconductor film having the crystalline structure withintense light.

Alternatively, a manufacturing method of the present inventioncomprises: a first step of adding a metal element to a firstsemiconductor film having an amorphous structure; a second step ofcrystallizing the first semiconductor film by first heat treatment toform a second semiconductor film having a crystalline structure; a thirdstep of forming an impurity region to which the element belonging to thegroup 15 of the periodic table, the element belonging to the group 13thereof, and the noble gas element are added in the second semiconductorfilm; a fourth step of performing gettering for segregating in theimpurity region the metal element contained in the second semiconductorfilm by second heat treatment after the third step; and a fifth step ofirradiating the semiconductor film having the crystalline structure withintense light.

Further, in the present invention, the metal element may be selectivelyadded using a mask made of a resist or a silicon oxide film.

Also, the present invention includes: a first step of selectively addinga metal element to a first region of a first semiconductor film havingan amorphous structure; a second step of crystallizing the firstsemiconductor film by first heat treatment to form a secondsemiconductor film having a crystalline structure; a third step ofadding a noble gas element to the first region in the secondsemiconductor film; a fourth region the metal element contained in thesecond semiconductor film by second heat treatment after the third step;and a fifth step of irradiating the semiconductor film having thecrystalline structure with intense light.

Alternatively, a manufacturing method of the present invention comprisesa first step of selectively adding a metal element to a first region ofa first semiconductor film having an amorphous structure; a second stepof crystallizing the first semiconductor film by first heat treatment toform a second semiconductor film having a crystalline structure; a thirdstep of adding a one conductivity type impurity element and a noble gaselement to the first region in the second semiconductor film; a fourthstep of performing gettering for segregating in the first region themetal element contained in the second semiconductor film by second heattreatment after the third step; and a fifth step of irradiating thesemiconductor film having the crystalline structure with intense light.

Alternatively, a manufacturing method of the present invention comprisesa first step of selectively adding a metal element to a first region ofa first semiconductor film having an amorphous structure; a second stepof crystallizing the first semiconductor film by first heat treatment toform a second semiconductor film having a crystalline structure; a thirdstep of adding an element belonging to the group 15 of the periodictable, an element belonging to the group 13 thereof, and a noble gaselement to the first region in the second semiconductor film; a fourthstep of performing gettering for segregating in the first region themetal element contained in the second semiconductor film by second heattreatment after the third step; and a fifth step of irradiating thesemiconductor film having the crystalline structure with intense light.

A semiconductor device manufactured through such steps is characterizedin that both the metal element and the noble gas element are containedin a one conductivity type impurity region. In addition, hydrogen may becontained in the one conductivity type impurity region.

Alternatively, a semiconductor device is characterized in that: a oneconductivity type impurity region and a channel forming region which isin contact with the one conductivity type impurity region are providedin a semiconductor film having a crystalline structure; and both themetal element and the noble gas element are contained in the oneconductivity type impurity region. In addition, hydrogen may becontained in the one conductivity type impurity region.

Alternatively, a semiconductor device is characterized in that: a secondimpurity region which is in contact with a first one conductivity typeimpurity region is provided; and the metal element and the noble gaselement are both contained in the second impurity region. In addition,hydrogen may be included in the second impurity region.

Alternatively, a semiconductor device is characterized in that: a firstone conductivity type impurity region, a second impurity region which isin contact with the first impurity region and a channel forming regionwhich is in contact with the first impurity region are provided in asemiconductor film having a crystalline structure; and the metal elementand the noble gas element are both contained in the second impurityregion. In addition, hydrogen may be contained in the second impurityregion.

Alternatively, a semiconductor device is characterized in that: a firstone conductivity type impurity region, a second impurity region which isin contact with the first impurity region; and a channel forming regionwhich is in contact with the first impurity region are provided in asemiconductor film having a crystalline structure and the metal element,the element belonging to the group 15 of the periodic table, the elementbelonging to the group 13 thereof, and the noble gas element arecontained in the second impurity region. In addition, hydrogen may becontained in the second impurity region.

In the above structure of the present invention, the metal element isone kind or plural kinds of elements selected from the group consistingof iron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh),palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), copper (Cu),and gold (Au).

In the above respective structures of the present invention, the intenselight is one of infrared light, visible light, or ultraviolet light.Also, the intense light indicates light which has a wavelength of 10 ìmor less and in which a main wavelength region is an infrared lightregion, and may be light emitted from, for example, a halogen lamp, ametal halide lamp, a xenon arc lamp, a carbon arc lamp, or a mercurylamp. A heat treatment method by the intense light using the above aslight sources is called rapid thermal anneal (hereinafter referred to asRTA) and known as a heat treatment technique for performing rapidheating for several microseconds of seconds to several tens. Further,the intense light may be light emitted from one of an excimer laser, aYAG laser, a YVO₄ laser, or a YLF laser. The intense light isirradiated, whereby the resistance value of the semiconductor filmhaving the crystalline structure can be reduced.

Also, the present invention provides a technique for forming thesemiconductor film having the crystalline structure. That is, there isprovided a method of manufacturing a semiconductor device, characterizedby comprising the steps of: adding a metal element to a semiconductorfilm having an amorphous structure; irradiating the semiconductor filmhaving the amorphous structure with first intense light to form asemiconductor film having a crystalline structure; irradiating thesemiconductor film having the crystalline structure with laser light;irradiating the semiconductor film having the crystalline structure withsecond intense light; forming an impurity region to which a noble gaselement is added in the semiconductor film having the crystallinestructure; and performing gettering for segregating in the impurityregion the metal element contained in the semiconductor film.

In the above structure, it is characterized in that the gettering stepis heat treatment.

Also, in the above structure, the gettering step may be processing forirradiating, the semiconductor film having the crystalline structurewith intense light. In this case, the semiconductor film having thecrystalline structure can be obtained without using a furnace.

Also, when heat treatment or intense light irradiation is performedplural times, flattening of a ridge formed in the semiconductor film canbe made.

Also, in the above structure, one kind or plural kinds of elementsselected from the group consisting of an element belonging to the group15 of the periodic table, an element belonging to the group 13 thereof,and hydrogen may be added in addition to the noble gas element.

A semiconductor device manufactured through such steps above comprises:a semiconductor region made from a crystalline semiconductor film; agate insulating film; and a gate electrode; a channel forming region andan impurity region which is in contact with the channel forming regionand to which a one conductivity type impurity element is added, areformed in the crystalline semiconductor film; and the one conductivitytype impurity region containing a noble gas element.

Alternatively, a semiconductor film comprises: a semiconductor regionmade from a crystalline semiconductor film; a gate insulating film; anda gate electrode; the crystalline semiconductor film having a channelforming region, a first impurity region which is in contact with thechannel forming region and to which a one conductivity type impurityelement is added, a second impurity region to which a one conductivitytype impurity element and a noble gas element are added.

Also, another structure comprises: a crystalline semiconductor filmformed by adding a metal element to a semiconductor film having anamorphous structure; a semiconductor region made of the crystallinesemiconductor film; a gate insulating film; a gate electrode; a channelforming region and an impurity region which is in contact with thechannel forming region and to which a one conductivity type impurityelement is added, formed in the crystalline semiconductor film, and thestructure is the one in which the one conductivity type impurity regioncontains a noble gas element and the metal element at a higherconcentration than the channel forming region.

Alternatively, another structure includes: a semiconductor region havinga crystalline semiconductor film produced by adding a metal element to asemiconductor film having an amorphous structure and made from thecrystalline semiconductor film; a gate insulating film; and a gateelectrode, the crystalline semiconductor film has a channel formingregion, a first impurity region which is in contact with the channelforming region and to which a one conductivity type impurity element isadded, and a second impurity region to which the one conductivity typeimpurity element and a noble gas element are added, and the secondimpurity region contains the metal element at a higher concentrationthan the channel forming region.

As described above, the present invention provides a technique forperforming gettering of a metal element contained in a semiconductorfilm using a noble gas element. Hereinafter, the present invention willbe described in more detail based on embodiment modes.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are explanatory views for a method of forming acrystalline semiconductor film according to the present invention;

FIGS. 2A to 2D are explanatory views for a method of forming acrystalline semiconductor film according to the present invention;

FIGS. 3A and 3B are explanatory views for a method of manufacturing asemiconductor device by a gettering method using a noble gas element;

FIGS. 4A to 4C are explanatory views for a method of manufacturing thesemiconductor device by the gettering method using the noble gaselement;

FIG. 5 is an explanatory view for a suitable concentration distributionfor the noble gas element implanted by an ion dope method;

FIGS. 6A to 6D are explanatory views for a method of manufacturing acrystalline semiconductor film according to the present invention;

FIGS. 7A to 7D are explanatory views for a method of manufacturing thecrystalline semiconductor film according to the present invention;

FIGS. 8A to 8C are explanatory views for a method of manufacturing thesemiconductor device by the gettering method using the noble gaselement;

FIGS. 9A to 9C are explanatory views for a method of manufacturing thesemiconductor device by the gettering method using the noble gaselement;

FIG. 10 is a graph indicating an etch pit density observed by FPMprocessing after the gettering;

FIG. 11 is a simple view indicating the etch pit density observed by theFPM processing after the gettering;

FIG. 12 is a graph indicating resistance values in the case where laserprocessing is performed after gettering;

FIGS. 13A to 13C2 are cross sectional views and a top surface view for astep of manufacturing a pixel portion;

FIGS. 14A to 14C2 are cross sectional views and a top surface view forthe step of manufacturing the pixel portion;

FIGS. 15A to 15C2 are cross sectional views and a top surface view forthe step of manufacturing the pixel portion;

FIGS. 16A to 16B2 are cross sectional views and a top surface view forthe step of manufacturing the pixel portion;

FIGS. 17A1 and 17A2 are a cross sectional view and a top surface viewfor the step of manufacturing the pixel portion;

FIG. 18 is a graph indicating an argon concentration profile in a depthdirection before and after anneal;

FIG. 19 is a graph indicating a nickel concentration profile in thedepth direction before and after the anneal;

FIG. 20 is a cross sectional view of the pixel portion;

FIG. 21 shows a measurement result by a SIMS analysis, indicating an Niconcentration in a semiconductor region having a width of 50 ìm beforesecond heat treatment;

FIG. 22 shows a measurement result by the SIMS analysis, indicating theNi concentration in the semiconductor region having the width of 50 ìmafter the second heat treatment;

FIGS. 23A through 23E are graphs indicating several characteristics of aTFT manufactured by gettering using argon;

FIGS. 24A to 24G show examples of a semiconductor device; and

FIGS. 25A to 25D show examples of the semiconductor device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described above, the present invention provides the technique forgettering the metal element included in the semiconductor film using thenoble gas element. Hereinafter, the present invention will be describedin details through the embodiment modes.

[Embodiment Mode 1]

FIGS. 1A to 1C are explanatory views of one embodiment mode of thepresent invention and show a method of adding a metal element havingcatalysis onto the entire surface of an amorphous semiconductor film tocrystallize it and then performing gettering. In FIG. 1A, bariumborosilicate glass, aluminoborosilicate glass, quartz, or the like canbe used for a substrate 101. An inorganic insulating film is formed as ablocking layer 102 with a thickness of 10 to 200 nm on the surface ofthe substrate 101. One example of a preferable blocking layer is asilicon oxynitride film produced by a plasma CVD method and a laminateof a first silicon oxynitride film produced from SiH₄, NH₃, and N₂O anda second silicon oxynitride film produced from SiH₄ and N₂O is applied.The first silicon oxynitride film and the second silicon oxynitride filmare formed with a thickness of 50 nm and with a thickness of 100 nm,respectively. The blocking layer 102 is provided so as not to diffusealkali metal included in the glass substrate into the semiconductor filmformed in this upper layer. When quartz is used for the substrate, theblocking layer can be omitted.

A semiconductor material including mainly silicon is used for asemiconductor film 103 having an amorphous structure, which is formed onthe blocking layer 102. Typically, an amorphous silicon film, anamorphous silicon germanium film, or the like is applied and formed witha thickness of 10 to 100 nm by a plasma CVD method, a low pressure CVDmethod, or a sputtering method. To obtain crystal having a good quality,it is necessary to minimize concentrations of impurities such as oxygen,nitrogen, and carbon, which are included in the semiconductor film 103having the amorphous structure. Thus, not only a high-purity, materialgas but also an ultra-high vacuum capable CVD apparatus are desirablyused.

Thereafter, a metal element having catalysis for promotingcrystallization is added onto the surface of the semiconductor film 103having the amorphous structure. The metal element having catalysis forpromoting crystallization of the semiconductor film is Fe, Ni, Co, Ru,Rh, Pd, Os, Ir, Pt, Cu, Au, or the like, and one kind or plural kinds ofelements selected from these elements can be used as the metal elements.Typically, nickel is used and a nickel acetate salt solution containingnickel at 1 to 10 ppm in weight conversion is applied by, a spinner toform a catalytic contained layer 104. In this case, in order to improveconformability of the solution, surface processing of the semiconductorfilm 103 having the amorphous structure is performed. That is, anextremely thin oxide film is formed using an aqueous solution containingozone and etched using a mixed solution of hydrofluoric acid andhydrogen peroxide solution to form a clean surface, and then processedagain using an aqueous solution containing ozone to form an extremelythin oxide film. Since the surface of a semiconductor film such assilicon is fundamentally hydrophobic, when the oxide film is formed asdescribed above, the nickel acetate salt solution can be uniformlyapplied.

Of course, a method of manufacturing the catalytic contained layer 104is not limited to such a method, and it may be formed by a sputteringmethod, an evaporation method or a plasma CVD method.

Next, heat treatment is performed at 500° C. for 1 hour to emit hydrogenincluded in the semiconductor film 103 having the amorphous structure.Then, heat treatment is performed for crystallization at 580° C. for 4hours. Thus, a crystalline semiconductor film 105 as shown in FIG. 1B isformed.

Further, in order to increase a crystallization ratio (ratio of acrystal component to the entire volume of a film) and to repair a defectleft in crystal grains, it is also effective to irradiate thecrystalline semiconductor film 105 with laser light. Excimer laser lighthaving a wavelength of 400 nm or less or the second harmonic or thethird harmonic of YAG laser light is used as the laser light. In anycase, pulse laser light having a repetition frequency of about 10 to1000 Hz is used and condensed at 100 to 400 mJ/cm² by an optical system,and thus laser processing to the crystalline semiconductor film 105 maybe performed at an overlap ratio of 90 to 95%.

Thus, the metal element (here, nickel) is left in the thus obtainedcrystalline semiconductor film 105. Although the distribution of themetal element is not uniform in the film, the metal element is left atan average concentration which exceeds 1×10¹⁹/cm³. Of course, even insuch a state, various semiconductor elements including a TFT can beformed. However, more preferably, it is desirable that the metal elementbe removed by gettering.

FIG. 1B shows a step of adding a noble gas element or this element and aone conductivity type impurity element to the crystalline semiconductorfilm by an ion dope method in order to form gettering sites 108. Asilicon oxide film 106 for masking is formed with a thickness of 100 to200 nm on a portion of the surface of the crystalline semiconductor film105, and the noble gas element or this element and the one conductivitytype impurity element are added to a region in which openings 107 areprovided and the crystalline semiconductor film is exposed. Theconcentration of the element in the crystalline semiconductor film isset to be 1×10¹⁹ to 1×10²¹/cm³.

One kind or plural kinds of elements selected from the group consistingof He, Ne, Ar, Kr, and Xe are used as the noble gas element. The presentinvention is characterized in that these inert gases are used as ionsources in order to form the gettering sites and implanted to thesemiconductor film by an ion dope method or an ion implantation method.The implantation of ions of these inert gases has two meanings. One isto form dangling bonds by the implantation to cause distortion in thesemiconductor film, and the other is to implant the ions betweenlattices of the semiconductor film to cause distortion therein. Theimplantation of ions by the inert gases can simultaneously satisfy boththe meanings. In particular, when an element such as Ar, Kr, or Xe,which has a larger atomic radius than silicon is used, the latter isremarkable obtained.

When heat treatment is performed for gettering in a nitrogen atmosphereat 450 to 800° C. for 1 to 24 hours, for example, at 550° C. for 14hours, the metal element can be segregated in the gettering sites 108.

Thereafter, when the gettering sites are removed by etching, acrystalline semiconductor film 109 in which the concentration of themetal element is reduced is obtained as shown in FIG. 1C. The thusformed crystalline semiconductor film 109 is made from an aggregation ofrod shaped or needle shaped crystals and the respective crystals growwith a specific orientation in a macroscopic view.

[Embodiment Mode 2]

A method of selectively forming a layer containing an element forpromoting crystallization of a semiconductor film will be described withreference to FIGS. 2A to 2D. In FIG. 2A, when a glass substrate is usedas a substrate 101, a blocking layer 102 is provided. Also, asemiconductor film 103 having an amorphous structure is formed in thesame manner as in Embodiment Mode 1.

Then, a silicon oxide film 110 having a thickness of 100 to 200 nm isformed on the semiconductor film 103 having the amorphous structure. Amethod of forming the silicon oxide film is not limited. For example,tetraethyl ortho silicate (TEOS) and O₂ are mixed and discharge isproduced at a reaction pressure of 40 Pa, a substrate temperature of 300to 400° C., and a high frequency (13.56 MHz) power density of 0.5 to 0.8W/cm, to form the silicon oxide film.

Next, openings 111 are formed in the silicon oxide film 110 and a nickelacetate solution including nickel at 1 to 10 ppm in weight conversion isapplied. Thus, a layer 112 containing a catalytic metal is formed andcome into contact with the semiconductor film 103 only on the bottomportions of the openings 111.

The crystallization shown in FIG. 1B is performed by heat treatment at aheating temperature of 500 to 650° C. for 4 to 24 hours, for example, at570° C. for 14 hours. In this case, silicides are formed in portions ofthe semiconductor film with which the metal element as a catalyst is incontact and the crystallization progresses from the silicides asnucleuses in a direction parallel to the surface of the substrate. Thethus formed crystalline silicon film 114 is made from an aggregation ofrod shaped or needle shaped crystals and the respective crystals growwith a specific orientation in a macroscopic view.

Next, a noble gas element or this element and a one conductivity typeimpurity element are added by an ion dope method using the openings 111to form gettering sites 115. When heat treatment is performed forgettering in a nitrogen atmosphere at 450 to 800° C. for 1 to 24 hours,for example, at 550° C. for 14 hours, the metal element can besegregated in the gettering sites 115. Thereafter, when the getteringsites are removed by etching, a crystalline semiconductor film 116 inwhich the concentration of the metal element is reduced is obtained asshown in FIG. 2D.

[Embodiment Mode 3]

A channel forming region and impurity regions such as a source regionand a drain region in a TFT can be formed using a semiconductor filmformed using a metal element having catalysis. Here, a method ofremoving the metal element from a channel forming region using theimpurity regions as gettering sites in TFT manufacturing steps will beexplained.

In FIG. 3A, a substrate 301, a blocking layer 302, and a semiconductorfilm 303 are formed similarly to Embodiment Modes 1 or 2. An insulatingfilm formed in the upper layer of the semiconductor film 303 is used asa gate insulating film of a TFT, and is made of silicon oxide or siliconoxynitride with a thickness of 30 to 150 nm, typically, 80 nm. A gateelectrode 305 is preferably made of a metal material such as tungsten,tantalum, titanium, or molybdenum or an alloy thereof.

In the case of an n-channel TFT, a donor, typically, phosphorus is addedto an impurity regions 306. Also, in the case of a p-channel TFT, boronis added as an acceptor to the impurity regions 306. In any case, theimpurity regions 306 can be formed by an ion dope method. In the case ofadding phosphorus, PH₃ is used. In the case of adding boron, B₂H₆ isused. These are generally diluted with hydrogen and supplied. In orderto use this impurity regions as effective gettering sites, a noble gaselement is implanted simultaneously with, before, or after the additionof the donor or the acceptor by an ion dope method.

Thereafter, as shown in FIG. 3B, a passivation film 308 is made from asilicon nitride film or a silicon oxynitride film and heat treatment isperformed in a nitrogen atmosphere at 450 to 800° C. for 1 to 24 hours,for example, at 550° C. for 14 hours. Thus, the impurity regions 306become the gettering sites, and the metal element can be segregated fromthe channel forming region into the gettering sites. Therefore, thedonor or the acceptor and the metal element are both present in theimpurity regions.

Also, as shown in FIG. 4A, after the blocking layer 302, thesemiconductor film 303, the insulating film 304, and the gate electrode305 are formed on or over the substrate 301, a mask 310 is formed. Then,one kind or plural kinds of elements belonging to group 18 of theperiodic table are added to the end portions of the semiconductor film303 using the mask 310 to form gettering sites 311.

Thereafter, a donor or an acceptor is added to form impurity regions312. Similarly, the donor or the acceptor is added to the getteringsites 311 and thus these are separately indicated as gettering sites313. Then, as shown in FIG. 4C, a passivation film 314 is made from asilicon nitride film or a silicon oxynitride film and heat treatment isperformed in a nitrogen atmosphere at 450 to 800° C. for 1 to 24 hours,for example, at 550° C. for 14 hours. Thus, the metal element can besegregated from the channel forming region into the gettering sites 313.

In a region of the semiconductor film to which the noble gas element isadded, the crystalline structure is broken and the region becomesamorphous. An element belonging to the group 18 of the periodic tabledoes not bond to silicon and is present between lattices. However, whenthe concentration of the element is high, the lattices are kept in adistorted state and thus it is difficult to recrystallize the region bylater heat treatment. On the other hand, for the purpose of forming thegettering sites, an effect for segregating the metal element is furtherenhanced with increasing the distortion. The structures shown in FIGS.4A to 4C correspond to a method of simultaneously satisfying both thematters and indicate an example in which the impurity regions forforming an element and the gettering sites are separately formed.

[Embodiment Mode 4]

FIG. 5 is an explanatory view of an addition of a noble gas elementintroduced into a semiconductor film in order to produce latticedistortion or lattice defect therein. The gettering described in FIGS.3A and 3B and FIGS. 4A to 4C indicates an example in which getteringsites are formed in a portion of an element forming region of asemiconductor film. In this case, it is considered that the getteringsites can be desirably recrystallized by heat treatment.

With respect to a semiconductor film including mainly silicon, a noblegas element having a high concentration often becomes a factor forhindering the recrystallization. To surely perform therecrystallization, it is necessary to focus attention on theconcentration distribution of an element to be implanted, belonging togroup 18 of the periodic table. In FIG. 5, structures of a semiconductorfilm 401, an insulating film 404, and a gate electrode 405 are similarto those in FIG. 3A. The element belonging to the group 18 is implantedinto the semiconductor film 401 through the insulating film 404.Although the concentration distribution of the implanted element isdependent on an accelerating voltage, the concentration distribution asindicated in a graph inserted into FIG. 5, along a thickness directionfrom the insulating film 404 to the semiconductor film 401 is obtained.

In the semiconductor film 401, the concentration of the noble gaselement becomes high in the insulating film 404 side and low in theopposite side. Whether or not it becomes amorphous is dependent on theconcentration of the element to be implanted, belonging to group 18.When the concentration is low, a crystalline portion can be left.Although the boundary cannot be clearly identified, as shown in FIG. 5,a region 402 to which an element belonging to the group 18 is added andwhich became amorphous can be distinguished from a region 403 to whichan element belonging to the group 18 is added but in which a crystallineportion is left.

If the region 403 in which the crystalline portion is left is present,it is easily recrystallized by heat treatment with gettering. That is,the region 403 in which the crystalline portion is left becomes anucleus for crystal growth and thus the crystallization of the region402 which became amorphous can be promoted. Such gettering sites can beeasily realized by controlling an accelerating voltage in an ion dopemethod. Even if the gettering sites are doped with a donor or anacceptor, it can be similarly realized.

Of course, the structure indicated by this embodiment mode can beapplied to the cases of forming the gettering sites in Embodiment Modes1 to 3.

[Embodiment Mode 5]

FIGS. 6A to 6D are explanatory views of another embodiment mode of thepresent invention and show a method of adding a metal element havingcatalysis onto the entire surface of an amorphous semiconductor film tocrystallize it and then performing gettering.

In FIG. 6A, barium borosilicate glass, aluminoborosilicate glass,quartz, or the like can be used for a substrate 101. An inorganicinsulating film is formed as a blocking layer 102 with a thickness of 10to 200 nm on the surface of the substrate 101. One example of apreferable blocking layer is a silicon oxynitride film produced by aplasma CVD method and a laminate of a first silicon oxynitride filmproduced from SiH₄, NH₃, and N₂O and a second silicon oxynitride filmproduced from SiH₄ and N₂O is applied. The first silicon oxynitride filmand the second silicon oxynitride film are formed with a thickness of 50nm and with a thickness of 100 nm, respectively. The blocking layer 102is provided so as not to diffuse alkali metal included in the glasssubstrate into the semiconductor film formed in the upper layer. Whenquartz is used for the substrate, the blocking layer can be omitted.

A semiconductor material including mainly silicon is used for asemiconductor film 103 having an amorphous structure, which is formed onthe blocking layer 102. Typically, an amorphous silicon film, anamorphous silicon germanium film, or the like is applied and formed witha thickness of 10 to 100 nm by a plasma CVD method, a low pressure CVDmethod, or a sputtering method. To obtain good quality crystal, it isnecessary to minimize concentrations of impurities such as oxygen,nitrogen, and carbon, which are included in the semiconductor film 103having the amorphous structure. Thus, not only a high purity materialgas but also an ultra-high vacuum capable CVD apparatus are desirablyused.

Thereafter, a metal element having catalysis for promotingcrystallization is added onto the surface of the semiconductor film 103having the amorphous structure. The metal element having catalysis forpromoting crystallization of the semiconductor film is iron (Fe), nickel(Ni), Cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium(Os), iridium (Ir), platinum (Pt), copper (Cu), gold (Au), or the likeand one kind or plural kinds of elements selected from these elementscan be used as the metal elements. Typically, nickel is used and anickel acetate solution including nickel at 1 to 10 ppm in weightconversion is applied by a spinner to form a catalytic contained layer104. In this case, in order to improve conformability of the solution,surface processing of the semiconductor film 103 having the amorphousstructure is performed. That is, an extreme thin oxide film is formedusing an aqueous solution containing ozone and etched using a mixedsolution of hydrofluoric acid and hydrogen peroxide solution to term aclean surface, and then processed again using an aqueous solutioncontaining ozone to form an extreme thin oxide film. Since the surfaceof a film of a semiconductor such as silicon is fundamentallyhydrophobic, when the oxide film is formed as described above, thenickel acetate solution can be uniformly applied.

Of course, a method of forming the catalytic contained layer 104 is notlimited to such a method, and it may be formed by a sputtering method,an evaporation method, or plasma processing.

Next, first intense light irradiation is performed for crystallization.Thus, a crystalline semiconductor film 105 shown in FIG. 6B is formed.Any one of infrared light, visible light, and ultraviolet light or acombination thereof can be used as the first intense light. Lightemitted from, typically, a halogen lamp, a metal halide lamp, a xenonarc lamp, a carbon arc lamp, a high pressure sodium lamp, or a highpressure mercury lamp is used (FIG. 6B). Note that, if necessary, heattreatment such that hydrogen contained in the semiconductor film 103having the amorphous structure is emitted may be performed before thefirst intense light irradiation.

Then, in order to increase a crystallization ratio (ratio of crystalcomponent to the entire volume of a film) and to repair a defect left incrystal grains, it is also effective to irradiate the crystallinesemiconductor film 105 with laser light. Excimer laser light having awavelength of 400 nm or less or the second harmonic or the thirdharmonic of YAG laser light is used as the laser light. In any case,pulse laser light having a repetition frequency of about 10 to 1000 Hzis used and condensed at 100 to 400 mJ/cm² by an optical system, andthus laser processing to the crystalline semiconductor film 105 may beperformed at an overlap ratio of 90 to 95%.

The metal element (here, nickel) is left in the crystallinesemiconductor film 105 thus obtained. Although the distribution of themetal element is not uniform in the film, the metal element is left atan average concentration which exceeds 1×10¹⁹/cm³. Of course even insuch a state, various semiconductor elements including a TFT can beformed. However, more preferably, the metal element is removed bygettering.

Further, second intense light irradiation is performed for thecrystalline semiconductor film 105 to disperse the metal element (here,nickel) into the film. Any one of infrared light, visible light, andultraviolet light or a combination thereof can be used as the secondintense light. Light emitted from, typically, a halogen lamp, a metalhalide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodiumlamp, or a high pressure mercury lamp is used.

FIG. 7A shows a step of adding a noble gas element or this element and aone conductivity type impurity element to a portion of the crystallinesemiconductor film 105 by an ion dope method in order to form impurityregions (hereinafter referred to as gettering sites) 108. In the case ofthe ion dope method, an Ar gas, a mixed gas of phosphine (PH₃) dilutedwith hydrogen and an Ar gas, a mixed gas of diborane (B₂H₆) diluted withhydrogen and an Ar gas, phosphine (PH₃) diluted with argon, or diborane(B₂H₆) diluted with argon can be used as a raw gas.

A silicon oxynitride film 106 for masking is formed with a thickness of100 to 200 nm on the surface of the crystalline semiconductor film 105by using a mask 107 made of a resist and a noble gas element or thiselement and a one conductivity type impurity element are added to aregion in which openings are provided and the crystalline semiconductorfilm is exposed. The concentration of the element in the crystallinesemiconductor film is set to be 1×10¹⁹ to 1×10²¹/cm³.

One kind or plural kinds of elements selected from the group consistingof helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) areused as the noble gas element. The present invention is characterized inthat these inert gases are used as ion sources in order to form thegettering sites and implanted to the semiconductor film by an ion dopemethod or an ion implantation method. The implantation of ions by theseinert gases has two meanings. One is to form dangling bonds by theimplantation to cause distortion in the semiconductor film and the otheris to implant the ions between lattices of the semiconductor film tocause distortion therein. The implantation of ions by the inert gasescan simultaneously satisfy both meanings. In particular, when an elementsuch as argon (Ar), krypton (Kr), or xenon (Xe), which has a largeratomic radius than silicon, is used, the latter is satisfied remarkably.Also, when the noble gas element is implanted, not only latticedistortion but also dangling bonds are produced and thus suchimplantation provides the gettering action. Further, when phosphorus asthe one conductivity type impurity element is implanted to thesemiconductor film in addition to the noble gas element, gettering canbe produced using Coulomb force of phosphorus. Furthermore, whenhydrogen is implanted to the semiconductor film in addition to the noblegas element, gettering can be produced using the produced danglingbonds.

Next, after the mask 107 made of a resist is removed, a gettering stepfor segregating the metal element included in the semiconductor filminto the gettering sites is performed (FIG. 7B).

As the gettering step, heat treatment is preferably performed in anitrogen atmosphere at 450 to 800° C. for 1 to 24 hours, for example, at550° C. for 14 hours. Intense light irradiation may be performed insteadof the heat treatment. Also, the intense light irradiation may beperformed in addition to the heat treatment. Note that, when an RTAmethod with light emitted from a halogen lamp, a metal halide lamp, axenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or ahigh pressure mercury lamp, as a heating means for gettering, is used,the intense light irradiation is desirably performed such that a heatingtemperature of the semiconductor film becomes 400° C. to 550° C. If theheating temperature is too high, the distortion in the semiconductorfilm is disappeared and an action for releasing nickel from nickelsilicide and an action for capturing nickel are lost, and thus getteringefficiency is reduced.

Then, the silicon oxynitride film 106 for masking is used for patterningof the crystalline semiconductor film without changing it. The getteringsites are removed by patterning to form the crystalline semiconductorfilm in a predetermined shape and then the silicon oxynitride film 106for masking is removed. Also, after the mask 106 is removed, heattreatment at 550° C. to 650° C. or intense light irradiation may beperformed to mainly planarize the surface of the semiconductor film.

Thus, as shown in FIG. 7C, the crystalline semiconductor film 109 inwhich the concentration of the metal element is reduced is obtained. Thecrystalline semiconductor film 109 formed by the above present inventionis made from an aggregation of rod shaped or needle shaped crystals andthe respective crystals grow with a specific orientation in amacroscopic view. The crystalline semiconductor film 109 is used as theactive layer of a TFT and thus a TFT as shown in FIG. 7D can becompleted.

When a minute semiconductor film is formed, only the noble gas elementis desirably added to perform gettering in this embodiment mode. In thecase where only the noble gas element is added to perform gettering,even if a minute semiconductor film is formed, TFT characteristic is notinfluenced, as compared with the case where gettering is produced usingphosphorus. Thus, such a case is effective.

[Embodiment Mode 6]

A method of selectively segrigating an element for promotingcrystallization of a semiconductor film will be described. When a glasssubstrate is used as a substrate, a blocking layer is provided. Asemiconductor film having an amorphous structure is also formedsimilarly to Embodiment mode 1.

Then, a silicon oxide film having a thickness of 100 to 200 nm is formedon the semiconductor film having the amorphous structure. A method offorming the silicon oxide film is not limited. For example, TEOS and O₂are mixed and discharge is produced at a reaction pressure of 40 Pa, asubstrate temperature of 300 to 400° C., and a high frequency (13.56MHz) power density of 0.5 to 0.8 W/cm², to form the silicon oxide film.

Next, openings are formed in the silicon oxide film and a nickel acetatesolution including nickel at 1 to 10 ppm in weight conversion isapplied. Thus, a layer containing a catalytic metal is formed and comeinto contact with the semiconductor film only in the bottom portions ofthe openings.

Then, crystallization is performed by heat treatment at a heatingtemperature of 500 to 650° C. for 4 to 24 hours, for example, at 570° C.for 14 hours. In this case, silicides are formed in portions of thesemiconductor film with which the metal element as a catalyst is incontact and the crystallization progresses from the silicides asnucleuses in a direction parallel to the surface of the substrate. Thethus formed crystalline silicon film is made from an aggregation of rodshaped or needle shaped crystals and the respective crystals grow with aspecific orientation in a macroscopic view.

Next, a noble gas element or this element and a one conductivity typeimpurity element are added by an ion dope method using the openings toform gettering sites. When heat treatment is performed for gettering ina nitrogen atmosphere at 450 to 570° C. for 1 to 24 hours, for example,at 550° C. for 14 hours, the metal element can be segregated in thegettering sites 115. Intense light irradiation may be performed insteadof the heat treatment. Also, the intense light irradiation may beperformed in addition to the heat treatment. Note that, when a RTAmethod with light emitted from a halogen lamp, a metal halide lamp, axenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or ahigh pressure mercury lamp, as a heating means for gettering, is used,the intense light irradiation is desirably performed such that a heatingtemperature of the semiconductor film becomes 400° C. to 550° C. If theheating temperature is too high, the distortion in the semiconductorfilm is disappeared and an action for releasing nickel from nickelsilicide and an action for capturing nickel are lost, and thus getteringefficiency is reduced.

Thereafter, when the gettering sites are removed by etching, acrystalline semiconductor film in which the concentration of the metalelement is reduced is obtained.

[Embodiment Mode 7]

A channel forming region and impurity regions such as a source regionand a drain region in a TFT can be formed using a semiconductor filmformed using a metal element having catalysis. Here, a method ofremoving the metal element from a channel forming region 207 using theimpurity regions as gettering sites in TFT manufacturing steps will bedescribed.

In FIG. 8A, a substrate 201, a blocking layer 202, and a semiconductorfilm 203 are formed similarly to any one of Embodiment Modes 1 and 2. Aninsulating film formed in the upper layer of the semiconductor film 203is used as a gate insulating film of a TFT and is made of silicon oxideor silicon oxynitride with a thickness of 30 to 150 nm, typically, 80nm. A gate electrode 205 is preferably made of a metal material such astungsten, tantalum, titanium, or molybdenum or an alloy thereof.

In the case of an n-channel TFT, a donor, typically, phosphorus is addedto impurity regions 206. Also, in the case of a p-channel TFT, anacceptor, boron is added to the impurity regions 206. In any case, theimpurity regions 206 can be formed by an ion dope method. In the case ofadding phosphorus, PH₃ is used. In the case of adding boron, B₂H₆ isused. These are generally diluted with hydrogen and supplied. In orderto use the impurity regions as effective gettering sites, a noble gaselement is implanted simultaneously with, before, or after the additionof the donor or the acceptor by an ion dope method. The impurity regions206 respectively become the source region and the drain region later.

In a region of the semiconductor film to which the noble gas element isadded, the crystalline structure is broken and the region becomesamorphous, the noble gas element does not bond to silicon and is presentbetween lattices. However, when the concentration of the element ishigh, the lattices are kept in a distorted state and thus it isdifficult to recrystallize the region by later heat treatment. On theother hand, for the purpose of forming the gettering sites, an effectfor segregating the metal element is further enhanced with increasingthe distortion.

Thereafter, as shown in FIG. 8B, a passivation film 208 is made from asilicon nitride film or a silicon oxynitride film and heat treatment isperformed in a nitrogen atmosphere at 450 to 800° C. for 1 to 24 hours,for example, at 550° C. for 14 hours. Thus, the impurity regions 206become the gettering sites and the metal element can be segregated fromthe channel forming region 207 into the impurity regions. Therefore, thedonor or the acceptor and the metal element coexist in the impurityregions. Note that, when the silicon oxynitride film is used as thepassivation film, hydrogen included in the passivation film is diffusedsimultaneously with gettering and thus the semiconductor film can behydrogenated. This step is a step of terminating dangling bonds in thesemiconductor film by hydrogen included in the passivation film.

The example in which gettering and hydrogenation are simultaneouslyperformed is described here. However, heat treatment for gettering andheat treatment for hydrogenation (heat treatment at, for example, 410°C.) may be performed in succession. Plasma hydrogenation (hydrogenexcited by plasma is used) may be performed as another means forhydrogenation.

Then, intense light is irradiated to activate an impurity element forproviding a one conductivity type, which is added to the impurityregions, and thus the resistance of the impurity regions is reduced.Since the passivation film is the silicon nitride film or the siliconoxynitride film, any one of YAG laser light (second harmonic or thirdharmonic) and intense light (light from lamp heating means) or acombination thereof is desirably used as the intense light. When thesilicon oxide is used for the passivation film, any one of excimer laserlight having a wavelength of 400 nm or less, YAG laser light (secondharmonic or third harmonic), and intense light (light from a lampheating means) and or a combination thereof can be used as the intenselight. Note that activation may be made by heat treatment. However,since recrystallization by only heat treatment is difficult as describedabove, intense light irradiation or both heat treatment and intenselight irradiation are desirably performed.

Then, an interlayer insulating film is formed, respective contact holeswhich reach the source region or the drain region are formed, and aconductive film is laminated. Thereafter, patterning is performed toform the source electrode and the drain electrode, and thus an n-channelTFT or a p-channel TFT is completed. A CMOS circuit can be formed bycombining an n-channel TFT and a p-channel TFT.

[Embodiment Mode 8]

Here, an example in which the manufacturing step order after the step offorming the passivation film is different from Embodiment Mode 3 will beindicated.

First, the same state as in FIG. 5B, which is described in EmbodimentMode 3 is obtained. Gettering is performed after the formation of apassivation film. When heat treatment is performed in a nitrogenatmosphere at 450 to 800° C. for 1 to 24 hours, for example, at 550° C.for 14 hours, the impurity regions become the gettering sites and themetal element can be segregated from the channel forming region into theimpurity regions. In the heat treatment for gettering, activation of animpurity element for providing a one conductivity type may be performed.Also, intense light irradiation may be performed instead of the heattreatment for gettering to simultaneously perform gettering andactivation of an impurity element. Note that, when a RTA method withlight emitted from a halogen lamp, a metal halide lamp, a xenon arclamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressuremercury lamp, as a heating means for gettering, is used, the intenselight irradiation is desirably performed such that a heating temperatureof the semiconductor film becomes 400° C. to 550° C. If the heatingtemperature is too high, the distortion in the semiconductor film isdisappeared and an action for releasing nickel from nickel silicide andan action for capturing nickel are lost, and thus gettering efficiencyis reduced.

Then, heat treatment is performed for hydrogenation in a nitrogenatmosphere at 300 to 550° C. for 1 to 12 hours, for example, at 410° C.for 1 hour. This step is a step of terminating dangling bonds in thesemiconductor film by hydrogen included in the passivation film.

Then, an interlayer insulating film is formed, respective contact holesWhich reach the source region or the drain region are formed, and aconductive film is laminated. Thereafter, patterning is performed toform the source electrode and the drain electrode, and thus an n-channelTFT or a p-channel TFT is completed. A CMOS circuit can be formed bycombining an n-channel TFT and a p-channel TFT.

[Embodiment Mode 9]

Here, an example in which the manufacturing step order after theaddition of a noble gas element and an impurity element for providing aone conductivity type is different from Embodiment Mode 3 will be shownin FIGS. 9A to 9C.

First, the same state as in FIG. 8A, which is described in EmbodimentMode 3 is obtained (FIG. 9A). As shown in FIG. 9A, a blocking layer 302,a semiconductor film 303, an insulating film 304, and a gate electrode305 are formed on or over a substrate 301. Then, any one kind or pluralkinds of noble gas elements are added to the end portions of thesemiconductor film 303 using the gate electrode 305 as a mask to formgettering sites. Thereafter, a donor or ran acceptor is added to thegettering sites to form impurity regions 306. The impurity regions 306respectively become the source region and the drain region later.

Next, as shown in FIG. 9B, when heat treatment is performed in anitrogen atmosphere at 450 to 800° C. for 1 to 24 hours, for example, at550° C. for 14 hours, the impurity regions 306 become the getteringsites, and the metal element can be segregated from the channel formingregion 307 into the gettering sites. In the heat treatment for thegettering, activation of an impurity element may be performed. Also,intense light irradiation may be performed instead of the heat treatmentfor the gettering to simultaneously produce gettering and activation.Note that, when an RTA method using light emitted from a halogen lamp ametal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressuresodium lamp, or a high pressure mercury lamp, as a heating means forgettering, is used, the intense light irradiation is desirably performedsuch that a heating temperature of the semiconductor film becomes 400°C. 550° C. If the heating temperature is too high, the distortion in thesemiconductor film is disappeared, and an action for releasing nickelfrom nickel silicide and an action for capturing nickel are lost, andthus gettering efficiency is reduced.

Then, as shown in FIG. 9C, a passivation film 308 is made from a siliconnitride film or a silicon oxynitride film and heat treatment isperformed for hydrogenation in a nitrogen atmosphere at 300 to 550° C.for 1 to 12 hours, for example, at 410° C. for 1 hour.

Then, an interlayer insulating film is formed, contact holes which reachthe source region or the drain region are formed, and a conductive filmis laminated. Thereafter, patterning is performed to form the sourceelectrode and the drain electrode, and thus an n-channel TFT or ap-channel TFT is completed. A CMOS circuit can be formed by combining ann-channel TFT and a p-channel TFT.

[Embodiment Mode 10]

Here, an example in which the surface of a semiconductor film having acrystalline structure, which is obtained by crystallizing an amorphoussemiconductor film by heat treatment or intense light irradiation, isetched in any one of Embodiment Modes 1 to 5 will be indicated.

For example, nickel silicide is removed by wet etching usinghydrofluoric acid system etchant and then laser light irradiation isperformed for anneal to the semiconductor film. Later steps areperformed according to Embodiment Modes 1 to 5 and a noble gas elementis preferably added to the semiconductor film having the crystallinestructure to perform gettering.

A mixed solution of hydrofluoric acid and hydrogen peroxide solution,FPM (mixed solution of hydrofluoric acid, hydrogen peroxide solution,and pure water), or the like is used as the above hydrofluoric acidsystem etchant.

[Embodiment 1]

In order to check the validity of the present invention, the followingexperiment is performed using argon as a noble gas element.

A crystalline semiconductor film crystallized by dehydrogenationprocessing at 500° C. for 1 hour and heat treatment at 550° C. for 4hours after a solution including nickel acetate at 10 ppm is applied toan amorphous silicon film with a thickness of 50 nm, is used as asemiconductor film. The crystalline semiconductor film is patterned andthen a silicon oxide film with a thickness of 90 nm is formed. A sampleproduced by implanting phosphorus into gettering sites by an ion dopemethod, a sample produced by implanting argon thereinto after theimplantation of phosphorus, and a sample produced by implanting onlyargon thereinto are prepared and evaluated by comparison. At this time,with respect to an implantation condition of phosphorus, PH₃ at 5%diluted with hydrogen is used, an accelerating voltage is set to be 80keV, and a dose is set to be 1.5×10¹⁵/cm². A time required forimplantation is about 8 minutes. Thus, phosphorus having an averageconcentration of 2×10²⁰cm³ can be implanted into the crystallinesemiconductor film. On the other hand, argon is implanted at anaccelerating voltage of 90 keV and a dose of 2×10¹⁵ or 4×10¹⁵/cm². Argonhaving a purity of 99.9999% or larger is used. It is sufficient that atime required for implantation is 1 to 2 minutes. These conditions arelisted in Table 1.

Table 1

Gettering is performed by heat treatment in a nitrogen atmosphere at550° C. for 4 hours. After the gettering, the silicon oxide film isremoved and then processed with FPM. A gettering effect is checked basedon the number of etch pits in a gettering region to be gettered of thecrystalline semiconductor film. That is, most of the added nickel isleft as nickel silicide in the crystalline semiconductor film, and it isknown that the nickel silicide is etched with FPM (mixed solution ofhydrofluoric acid, hydrogen peroxide solution, and pure water).Therefore, the gettering region to be gettered is processed with the FPMand it is examined whether an etch pit is present or not, and thus thegettering effect can be checked. In this case, the smaller the number ofetch pits is, the higher the gettering effect is. FIG. 11 is a simpleview of a sample in which an etch pit is produced. Note that, in FIG.11, a dope region indicates a region to which argon or phosphorus isadded. The number of etch pits present in the gettered region (getteringregion to be gettered) is counted while observing it using an opticalmicroscope to obtain an etch pit density.

FIG. 10 shows its result. In FIG. 10, a sample indicated by P is asample to which only phosphorus is added. With respect to a phosphorusimplantation condition of this sample, PH₃ at 5% diluted with hydrogenis used, an accelerating voltage is set to be 80 keV, and a dose is setto be 1.5×10¹⁵/cm². Also, in FIG. 10, a sample indicated by P+Ar (1 min)is a sample to which phosphorus and argon are added. With respect to aphosphorus implantation condition of this sample, PH₃ at 5% diluted withhydrogen is used, an accelerating voltage is set to be 80 keV and a doseis set to be 1.5×10¹⁵/cm². With respect to an argon implantationcondition, an accelerating voltage is set to be 90 keV, a dose is set tobe 2×10¹⁵/cm², and a time required for argon implantation is set to be 1minute. Further, in FIG. 10, a sample indicated by P+Ar (2 min) is asample to which phosphorus and argon are added. With respect to aphosphorus implantation condition of this sample, PH₃ at 5% diluted withhydrogen is used, an accelerating voltage is set to be 80 keV, and adose is set to be 1.5×10¹⁵/cm². With respect to an argon implantationcondition, an accelerating voltage is set to be 90 keV, a dose is set tobe 4×10¹⁵/cm², and a time required for argon implantation is set to be 2minutes. Furthermore, in FIG. 10, a sample indicated by Ar is a sampleto which only argon is added. With respect to an argon implantationcondition of this sample, an accelerating voltage is set to be 90 keVand a dose is set to be 2×10¹⁵/cm².

From the result of the experiment shown in FIG. 10, it is apparent thatalthough the sample to which only phosphorus is added has an etch pitdensity of 3.5×10⁻³/ìm², the sample in which argon is added to andgettering is performed has the number of etch pits (etch pit density) of5×10⁻⁴/ìm² or smaller, and thus the number of etch pits is decreased toan extreme. This result indicates that the gettering effect is improvedto an extreme by argon implantation. Therefore, it is indicated thatgettering using non metal elements (one kind or plural kinds of elementsselected from the group consisting of B, Si, P, As, He, Ne, Ar, Kr, andXe) according to the present invention is extremely effective.

[Embodiment 2]

In this embodiment, an example in which argon is added to gettering isperformed and then laser light irradiation is performed will beindicated.

First, a sample is produced as in Embodiment 1. A crystallinesemiconductor film crystallized by dehydrogenation processing at 500° C.for 1 hour and heat treatment at 550° C. for 4 hours after a solutionincluding nickel acetate at 10 ppm is applied to all amorphous siliconfilm with a thickness of 50 nm, is used as a semiconductor film. Thecrystalline semiconductor film is patterned and then a silicon oxidefilm with a thickness of 90 nm is formed. Next by passing the siliconoxide film with a thickness of 90 nm, argon is implanted to thecrystalline semiconductor film after phosphorus is implanted. At thistime, with respect to an implantation condition of phosphorus, PH₃ at 5%diluted with hydrogen is used, an accelerating voltage is set to be 80keV, and a dose is set to be 1.5×10¹⁵/cm². A time required forimplantation is about 8 minutes. Thus, phosphorus having an averageconcentration of 2×10²⁰/cm³ can be implanted into the crystallinesemiconductor film. On the other hand, argon is implanted at anaccelerating voltage of 90 keV and a dose of 2×10¹⁵ or 4×10³/cm². Then,heat treatment is performed for gettering in a nitrogen atmosphere at550° C. for 4 hours.

Then, a laser energy condition is changed, and excimer laser light isirradiated. The result of the experiment after the subsequent sheetresistance measurement is shown in FIG. 12. As shown in FIG. 12, a sheetresistance value can be reduced to such a level that no problem iscaused in a device characteristic by the laser light irradiation.

Note that, in this embodiment, laser light from a pulse oscillation typeexcimer laser is used. However, the present invention is notparticularly limited to such a laser, and a continuous light emissiontype excimer laser, a YAG laser, or a YVO₄ laser may be used. A rapidthermal anneal method (RTA method) may be applied instead of a laseranneal method.

Note that this embodiment can be combined with any one of EmbodimentModes 1 to 10.

[Embodiment 3]

In this embodiment, an example in which the present invention is appliedto a double gate TFT and an active matrix substrate using the doublegate TFT as a TFT of a pixel portion is manufactured is shown in FIGS.13A to 13C2.

First, a conductive film is formed on a substrate 401 having aninsulating surface and patterned to form a scan line 402. The scan line402 also severs as a light shielding layer for protecting an activelayer formed later from light. Here, a quartz substrate is substrate isused as the substrate 401. Also, a laminate structure of a polysiliconfilm (50 nm in a film thickness) and a tungsten silicide (W—Si) film(100 nm in a film thickness) is used as the scan line 402. Thepolysilicon film is to prevent a contamination from the tungstensilicide to the substrate.

Then, insulating films 403 a and 403 b covering the scan line 402 areformed with a film thickness of 100 to 1000 nm (typically 300 to 500nm). Here, a silicon oxide film having a film thickness of 100 nm and asilicon oxide film having a film thickness of 280 nm using a CVD methodand an LPCVD method, respectively, are laminated.

Then, an amorphous semiconductor film is formed with a film thickness of10 to 100 nm. Here, the amorphous silicon film is formed with a filmthickness of 69 nm by an LPCVD method. Then, the amorphous silicon filmis crystallized using the technique for crystallizing this amorphoussemiconductor film described in Japanese Patent Application Laid-openNo. Hei 8-78329. According to the described technique, a metal elementfor promoting crystallization is selectively added to an amorphoussilicon film, and heat treatment is performed to form such a crystallinesilicon film in which the crystallization is expanded from an addedregion as a starting point. Here, nickel is used as the element forpromoting crystallization. Also, after heat treatment fordehydrogenation (at 450° C., for 1 hour), heat treatment forcrystallization (at 600° C., for 12 hours) is performed.

Then, a gettering site 404 b for gettering Ni from a region as theactive layer of a TFT is formed. The region as the active layer of theTFT is covered with a mask (silicon oxynitride film) 400 and a noble gaselement, here, argon (Ar) is added to a portion of the crystallinesilicon film (FIG. 13A). Note that the mask 400 is also used in the caseof patterning the crystalline silicon film later. Further, when only thenoble gas element is added as this embodiment, since the influence on anelectrical characteristic and the like of a TFT is small as comparedwith the case of adding phosphorus, the region as the active layer ofthe TFT can be formed into a minute size. Thus, a finer design of a TFTis possible.

Further, the noble gas element may be added in a state in which theresist mask used at the formation of the mask 400 is left.

Further, one kind or plural kinds of elements selected from the groupconsisting of an element belonging to the group 15 of the periodictable, an element belonging to the group 13 thereof, silicon, andhydrogen may be added to the portion of the crystalline silicon film inaddition to the noble gas element.

Then, heat treatment for gettering Ni from the region as the activelayer of the TFT (in a nitrogen atmosphere at 550° C., for 4 hours) isperformed (FIG. 13B). By this heat treatment, the metal (Ni) included inthe crystalline silicon film is moved from the region as the activelayer of the TFT in the direction of an arrow in FIG. 13B and capturedin the gettering site (region to which the noble gas element is added).Thus, the metal (Ni) is removed from the crystalline silicon film exceptfor the gettering site, or reduced.

Then, after the mask is removed and patterning is performed to remove anunnecessary portion of the crystalline silicon film, thereby forming asemiconductor film 404 (FIG. 13C1). Note that a top surface view of apixel after the formation of the semiconductor film 404 is shown in FIG.13C2. In FIG. 13C2, a cross sectional view obtained by cutting along adotted line A–A′ corresponds to FIG. 13C1.

Then, in order to form a retaining capacitor, a mask 405 is formed and aportion of the semiconductor film (a region for the retaining capacitor)406 is doped with phosphorus (FIG. 14A).

Then, after the mask 405 is removed and an insulating film covering thesemiconductor film is formed, a mask 407 is formed and an insulatingfilm on the region 406 for the retaining capacitor is removed (FIG.14B).

Then, the mask 407 is removed and thermal oxidation is performed to forman insulating film (gate insulating film) 408 a. A final film thicknessof the gate insulating film becomes 80 nm by this thermal oxidation.Note that an insulating film 408 b thinner than in other region of theinsulating film is formed on the region for the retaining capacitor(FIG. 14C1). A top surface view of a pixel at this time is shown in FIG.14C2. In FIG. 14C2, a cross sectional view obtained by cutting along adotted line B–B′ corresponds to FIG. 14C1. Also, a region indicated bychain lines in FIGS. 14C2 is a portion in which the thin insulating film408 b is formed.

Then, a channel dope step of entirely or selectively adding a p-type oran n-type impurity element at a low concentration to a region as thechannel region of the TFT is performed. This channel dope step is a stepfor controlling a TFT threshold value voltage. Note that boron is addedby an ion dope method using plasma excitation without mass separation ofdiborane (B₂H₆). Of course, an ion implantation method performing massseparation may also be used.

Then, a mask 409 is formed on or over the insulating films 408 a, 403 a,and 403 b and a contact hole which reaches the scan line 402 is formed(FIG. 15A). After the formation of the contact hole, the mask isremoved.

Then, a conductive film is formed and patterned to form a gate electrode410 and a capacitor wiring 411 (FIG. 15B). Here, a laminate structure ofa silicon film (150 nm in a film thickness) doped with phosphorus andtungsten silicide (150 nm in a film thickness) is used. Note that, aretaining capacitor is composed of the insulating film 408 b asdielectric, the capacitor wiring 411, and a portion of the semiconductorfilm 406.

Then, phosphorus is added at a low concentration in a self alignmentmanner using the gate electrode 410 and the capacitor wiring 411 asmasks (FIG. 15C1). A top surface view of a pixel at this time is shownin FIG. 15C2. In FIG. 15C2, a cross sectional view obtained by cuttingalong a dotted line C–C′ corresponds to FIG. 15C1. A concentration ofphosphorus in a region added at a low concentration of phosphorus iscontrolled to be 1×10¹⁶ to 5×10¹⁸ atoms/cm³, typically, 3×10¹⁷ to 3×10¹⁸atoms/cm³.

Then, a mask 412 is formed and phosphorus is added thereto with the mask412 at a high concentration to form high concentration impurity regions413 respectively as a source region or a drain region (FIG. 16A). Aconcentration of phosphorus in this high concentration impurity regionsis controlled to be 1×10²⁰ to 1×10²¹ atoms/cm³ (typically 2×10²⁰ to5×10²⁰ atoms/cm³). Note that, in the semiconductor film 404, a regionoverlapped with the gate electrode 410 becomes a channel forming region414, and regions covered with the mask 412 become low concentrationimpurity regions 415 and function as LDD regions. Alter the addition ofthe impurity element, the mask 412 is removed.

Then, although not shown here, in order to form a p-channel TFT used fora driver circuit formed on the same substrate as a pixel, a region as ann-channel TFT is covered with a mask, and boron is added to form thesource region or the drain region.

Next, after the mask 412 is removed, a passivation film 416 which coversthe gate electrode 410 and the capacitor wiring 411 is formed. Here, asilicon oxide film is formed with a film thickness of 70 nm. Then, aheat treatment step of activating an n-type or a p-type impurity elementadded to the semiconductor film at respective concentrations isperformed. Here, heat treatment is performed at 850° C. for 30 minutes.

Then, an interlayer insulating film 417 made of an organic resinmaterial is formed. Here, an acrylic resin film having a film thicknessof 400 nm is used. Thereafter, contact holes which reach thesemiconductor film are formed and an electrode 418 and a source wiring419 are formed. In this embodiment, the electrode 418 and the sourcewiring 419 respectively are made from a laminate film having a threelayers structure, in which a Ti film with a thickness, of 100 nm, analuminum film containing Ti with a thickness of 300 nm, and a Ti filmwith a thickness of 150 nm are formed in succession by a sputteringmethod (FIG. 16B). Note that, in FIG. 16B2, a cross sectional viewobtained by cutting along a dotted line D–D′ corresponds to FIG. 16B1.

Then, after hydrogenation processing, an interlayer insulating film 420made of acrylic is formed (FIG. 17A1). Then, a conductive film having alight shielding characteristic is formed with a film thickness of 100 nmon the interlayer insulating film 420 to form a light shielding layer421. Thereafter, an interlayer insulating film 422 and a contact holewhich reaches the electrode 418 are formed. A transparent conductivefilm (here, indium tin oxide (ITO) film) with a thickness of 100 nm isformed and then patterned to form pixel electrodes 423 and 424. In FIG.17A2, a cross sectional view obtained by cutting along a dotted lineE–E′ corresponds to FIG. 17A1.

Thus, a pixel TFT made from an n-channel TFT is formed in the pixelportion while keeping an area (aperture ratio is 76.5%) of a displayregion (26 ìm×26 ìm in the pixel size) and a sufficient retainingcapacitance (51.5 fF) can be obtained.

Note that this embodiment is one example, and the present invention isnot limited to the steps of this embodiment. For example, an elementselected from the group consisting of tantalum (Ta), titanium (Ti),molybdenum (Mo), tungsten (W), chromium (Cr), and silicon (Si) or analloy of a combination of the elements (typically, an Mo—W alloy or anMo—Ta alloy) can be used as the respective conductive film. Also, asilicon oxide film, a silicon nitride film, a silicon oxynitride film,or an organic resin material (polyimide, acrylic, polyamide,polyimideamide, BCB (benzocyclobutene), or the like) film can be used asthe respective insulating films.

Thus, the pixel portion having the n-channel TFT and the retainingcapacitor and the driver circuit (not shown) having a CMOS circuitcomposed of the n-channel TFT and the p-channel TFT can be formed on thesame substrate. In this specification, such a substrate is called anactive matrix substrate for convenience.

Next, a step of manufacturing a liquid crystal module using the obtainedactive matrix substrate will be described below.

An orientation film is formed on the active matrix substrate shown inFIG. 17A1 and rubbing processing is performed. Note that, in thisembodiment, an organic resin film such as an acrylic resin film ispatterned before the formation of the orientation film to formcolumn-shaped spacers for keeping a substrate interval in predeterminedpositions. Instead of the column-shaped spacers, spherical spacers maybe spread on the entire surface of the substrate.

Then, a counter substrate is prepared. A color filter in which coloredlayers and a light shielding layer are arranged corresponding to eachpixel is provided in the counter substrate. Further, a light shieldinglayer is also provided in the driver circuit portion. A planarizing filmis provided to cover this color filter and the light shielding layer.Thereafter, a counter electrode made from a transparent conductive filmis formed in the pixel portion on the planarizing film, an orientationfilm is formed on the entire surface of the counter substrate, andrubbing processing is performed.

The active matrix substrate in which the pixel portion and the drivercircuit are formed is adhered to the counter substrate by a sealingmaterial. Fillers are mixed into the sealing materials. Two substratesare adhered to each other with keeping a constant interval by thefillers and the column-shaped spacers. Thereafter, a liquid crystalmaterial is injected between both the substrates and complete sealing isperformed by a sealing a gent. A known liquid crystal material ispreferably used as the liquid crystal material to be injected. Thus, theliquid crystal module is completed. If necessary, the active matrixsubstrate or the counter substrate is cut into a desired shape. Further,a polarizing plate and the like are suitably provided using a knowntechnique. Then, an FPC is adhered using a known technique.

The liquid crystal module thus manufactured can be used as a displayportion of various electronic devices.

Note that this embodiment can be combined with any one of EmbodimentModes 1 to 10.

[Embodiment 4]

In order to check the validity of the present invention, the followingexperiment is performed using argon (Ar) of non metal elements (one kindor plural kinds of elements selected from the group consisting of B, Si,P, As, He, Ne, Ar, Kr, and Xe).

An amorphous silicon film is formed with a film thickness of 400 nm on asubstrate and a metal element (nickel) having catalytic for promotingcrystallization is added onto the surface of the amorphous silicon film.A nickel acetate solution including nickel at 100 ppm in weightconversion is applied to the amorphous silicon by a spinner to form acatalytic contained later. After heat treatment at 500° C. for 1 hour,heat treatment is further performed at 550° C. for 12 hours to form asilicon film having a crystalline structure.

An argon element is added to the thus obtained silicon film having thecrystalline structure. Here, an ion doping method is used to add anargon element. An argon gas is used as a raw gas in condition that anaccelerating voltage is 10 keV, a flow rate is 50 sccm a current densityis 1 ìA/cm², and a dose is 2×10¹⁵ atoms/cm². Note that the argon elementis added only by a depth of about 0.05 ìm from the surface in thisdoping condition. Then, heat treatment (anneal) is performed forgettering at 550° C. for 4 hours.

A concentration distribution (by SIMS measurement) of the argon elementafter addition and a concentration distribution (by SIMS measurement) ofthe nickel element after addition are shown in FIGS. 18 and 19,respectively, using a solid line indicating a concentration distributionbefore anneal. Note that, in FIGS. 18 and 19, abscissa indicates a depthand ordinate indicates a concentration. The concentration distribution(by SIMS measurement) of the argon element after anneal and theconcentration distribution (by SIMS measurement) of the nickel elementafter anneal are shown in FIGS. 18 and 19, respectively, using a dottedline indicating a concentration distribution after anneal.

From experimental results shown in FIGS. 18 and 19, it is apparent thatthe concentration distribution of the argon element is not varied beforeand after anneal but the concentration distribution of the nickelelement is varied before and after the anneal. In the region to whichthe argon element is added by a depth of about 0.05 ìm, a maximum nickelconcentration after anneal becomes 6×10¹⁹ atoms/cm³. Also, in a regionto which the argon element is not added, although the nickelconcentration before anneal is about 5×10¹⁸ atoms/cm³, the nickelconcentration after anneal is about 1×10¹⁸ atoms/cm³ and reduced to aminimum nickel concentration of 4×10¹⁷ atoms/cm³.

This result means that the region to which argon is added by a depth ofabout 0.05 ìm from the surface acts as gettering sites by annealprocessing, the nickel element in the film is moved to the getteringsites, and thus the nickel element in the region to which argon is notadded is reduced.

That is, the experimental result of this embodiment means that anneal isperformed after the implantation of argon and thus the gettering effectis extremely high and it is indicated that gettering using non metalelements (one kind or plural kinds of elements selected from the groupconsisting of B, Si, P, As, He, Ne, Ar, Kr, and Xe) according to thepresent invention is extremely effective.

The concentration of the argon element is not varied. Thus, in the casewhere the gettering sites to which the argon element is added is used asa portion of the semiconductor film without processing and a TFT ismanufactured using the semiconductor film, when heat treatment in a TFTmanufacturing step after gettering is performed, the gettering effectcan be continuously obtained. Also, since the gettering sites are heatedby heat produced when the completed TFT is driven, the gettering effectcan be continuously obtained.

[Embodiment 5]

The example of a transmission type is described in Embodiment 4. In thisembodiment, an example of a reflection type is shown in FIG. 20. In thisembodiment, a reflection electrode is used as a pixel electrodeconnected with the drain region of a TFT in the pixel portion.

A pixel electrode is used as the electrode 418 in Embodiment 4 and areflection electrode 1001 as a pixel electrode is formed. Thisreflection electrode is made from a material having superior reflectingproperty, such as a film including mainly Al or Ag or laminate filmthereof. After the formation of the pixel electrode, preferably, a stepsuch as a known sand blast method or a known etching method is added toproduce unevenness of the surface, and thus a mirror reflection isprevented and reflected light is scattered to increase a whitenessdegree.

Note that this embodiment can be combined with any one of EmbodimentModes 1 to 5.

[Embodiment 6]

A crystalline semiconductor film formed by implementing the presentinvention is used for an active layer of a TFT, and the TFT can be usedfor various modules (a liquid crystal display device, a light emittingtype display device, an active matrix type EC display, DMD (digitalmicromirror device) or the like). That is, the present invention can beimplemented in all the electronic devices in which those modules areincorporated into their display portions.

FIG. 24A is an example of completing a television receiver by applyingthe present invention, and is composed of a housing 3001, a supportingstand 3002, a display portion 3003 and the like. A TFT substratemanufactured by the present invention is applied to the display portion3003, and the television receiver can be completed by the presentinvention.

FIG. 24B is an example of completing a video camera by applying thepresent invention, and is composed of a main body 3011, a displayportion 3012, an audio input portion 3013, operation switches 3014, abattery 3015, an image receiving portion 3016 and the like. The TFTsubstrate manufactured by the present invention is applied to thedisplay portion 3012, and the video camera can be completed by thepresent invention.

FIG. 24C is an example of completing a note type personal computer byapplying the present invention, and is composed of a main body 3021, ahousing 3022, a display portion 3023, a keyboard 3024 and the like. TheTFT substrate manufactured by the present invention is applied to thedisplay portion 3023, and the personal computer can be completed by thepresent invention.

FIG. 24D is an example of completing a PDA (Personal Digital Assistant)by applying the present invention, and is composed of a main body 3031,a stylus 3032, a display portion 3033, operation buttons 3034, anexternal interface 3035 and the like. The TFT substrate manufactured bythe present invention is applied to the display portion 3033, and thePDA can be completed by the present invention.

FIG. 24E is an example of completing a sound reproducing apparatus byapplying the present invention. More specifically, it is an audioapparatus for automobile use, and is composed of a main body 3041, adisplay portion 3042, operation switches 3043 and 3044 and the like. TheTFT substrate manufactured by the present invention is applied to thedisplay portion 3042, and the audio apparatus can be completed by thepresent invention.

FIG. 24F is an example of completing a digital camera by applying thepresent invention, and is composed of a main body 3051, a displayportion A 3052, an eye piece portion 3053, operation switches 3054, adisplay portion B 3055, a battery 3056 and the like. The TFT substratemanufactured by the present invention is applied to the display portionA 3052 and the display portion B 3055, and the digital camera can becompleted by the present invention.

FIG. 24G is an example of completing a portable telephone by applyingthe present invention, and is composed of a main body 3061, an audiooutput portion 3062, an audio input portion 3063, a display portion 3064operation switches 3065 an antenna 3066 and the like. The TFT substratemanufactured by the present invention is applied to the display portion3064, and the portable telephone can be completed by the presentinvention.

FIG. 25A shows a front type projector, which contains components such asa projecting apparatus 2601 and a screen 2602. FIG. 25B shows a reartype projector, which contains components such as a main body 2701, aprojecting apparatus 2702, a mirror 2703, and a screen 2704.

Note that an example of the structure of the projecting apparatuses 2601and 2702 of FIG. 25A and FIG. 25B is shown in FIG. 25C. The projectingapparatuses 2601 and 2702 are composed of a light source optical system2801, mirrors 2802 and 2804 to 2806, a dichroic mirror 2803, a prism2807, a liquid crystal display device 2808, a phase difference plate2809, and a projecting optical system 2810. The projecting opticalsystem 2810 is composed or an optical system including a projectinglens. A three-plate type example is shown in the present embodiment, butthere are no particular limitations, and a single-plate type may also beused, for example. Further, optical systems such as an optical lens, afilm having a light polarizing function, a film for regulating the phasedifference, and an IR film may be suitably placed in an optical pathshown by an arrow in FIG. 25C by an operator.

Furthermore, FIG. 25D is a diagram showing one example of the lightsource optical system 2801 in FIG. 25C. In the present embodiment, thelight source optical system 2801 is composed of a reflector 2811, alight source 2812, lens arrays 2813 and 2814, a polarizingtransformation element 2815, and a condenser lens 2816. Note that thelight source optical system shown in FIG. 25D is one example, and thelight source optical system is not limited to the structure shown in thefigure. For example, optical systems such as an optical lens a filmhaving a light polarizing function, a film for regulating the phasedifference and an IR film may be suitably placed in the light sourceoptical system by an operator.

Note that, the electronic devices exemplified in the above is only anexample, and the present invention is not limited to those use.

[Embodiment 7]

With respect to the crystalline semiconductor film obtained by the stepsshown in FIGS. 6A to 6D and 7A to 7D, a gettering effect of a metalelement used as a catalyst in crystallization. Using argon as a noblegas element, is shown in FIGS. 21 and 22.

The crystalline semiconductor film formed in this embodiment is obtainedby the following steps. That is, an amorphous silicon film with athickness of 50 nm is deposited on a quartz substrate by a reducedpressure CVD method, Ni is added thereto at 5 ppm, dehydrogenationprocessing is performed at 450° C. for 1 hour, and then first heattreatment is performed at 600° C. for 12 hours to crystallize theamorphous silicon film. Thereafter, a mask insulating film as a siliconoxide film having openings is formed and argon ions are implantedthrough the openings at 10 kV and a dose of 2×10¹⁵/cm³. Second heattreatment is performed at 550° C. for 4 hours to segregate Ni in theregion to which argon ions are implanted. An interval between theopenings is 50 ìm. The concentration of nickel in a semiconductor regioncovered with the mask insulating film is quantitatively evaluated.

FIG. 21 shows a result obtained by measuring the concentration of Nibefore the second heat treatment by a SIMS analysis and FIG. 22 shows aresult of the concentration of Ni after the second heat treatment. Ascan be seen from these two graphs, it is clearly indicated that theconcentration of Ni is reduced by the second heat treatment and thegettering effect is produced.

FIGS. 23A through 23E are graphs indicating several characteristics ofan n-channel TFT manufactured using such a crystalline semiconductorfilm. A channel length and a channel width of the TFT are 8 ìm and 8 ìm,respectively. Even in the case of comparison of TFT characteristicsgettered by phosphorus and argon, characteristics of TFT gettered byargon are almost the same as characteristics of TFT gettered byphosphorus, and thus similar gettering effect as one by phosphorus canbe obtained by using argon of about 2×10¹⁵ to 6×10¹⁵/cm².

As described above, according to the intrinsic gettering performed byimplanting the element belonging to the group 18 of the periodic tableto the semiconductor film in the present invention, an effect such thatthe metal element left in the crystalline semiconductor film is getteredis extremely high. This can produce an increase in a purity of thecrystalline semiconductor film formed using the metal element having acatalytic action and an improvement in productivity of a semiconductordevice using the crystalline semiconductor film. The noble gas elementis easy to use even in the case of ion doping. Since the noble gaselement can be used without diluting it with a balance gas or the like,there is a characteristic such that a time required for doping isshortened.

Also, according to the intrinsic gettering performed by implanting thenoble gas element to the semiconductor film in the present invention, aneffect such that the metal element left in the crystalline semiconductorfilm is gettered is extremely high. This can produce an increase in apurity of the crystalline semiconductor film formed using the metalelement having a catalytic action and an improvement in productivity ofa semiconductor device using the crystalline semiconductor film. Thatis, the noble gas element is an inert gas and easy to use even in thecase of ion doping. Further, there is a characteristic such that a timerequired for doping is shortened.

TABLE 1 P dope condition Ar dope condition sample acceleratingaccelerating No. voltage dose voltage dose 1 80 keV 1.5 × 10¹⁵/cm² — — 280 keV 1.5 × 10¹⁵/cm² 90 keV 2.0 × 10¹⁵/cm² 3 80 keV 1.5 × 10¹⁵/cm² 90keV 4.0 × 10¹⁵/cm² 4 — — 90 keV 2.0 × 10¹⁵/cm²

1. A method of manufacturing a semiconductor device comprising the stepsof: adding a metal element to a semiconductor film having an amorphousstructure; crystallizing the semiconductor film by a first heattreatment to form a crystalline semiconductor film; forming an impurityregion to which a noble gas element is selectively added in thecrystalline semiconductor film; and segregating the metal element in theimpurity region containing the noble gas element by a second heattreatment.
 2. A method of manufacturing a semiconductor device accordingto claim 1, wherein the first heat treatment is performed by a rapidthermal anneal method using one heat source selected from the groupconsisting of a halogen lamp, a metal halide lamp, a xenon arc lamp, anda carbon arc lamp.
 3. A method of manufacturing a semiconductor deviceaccording to claim 1, wherein the second heat treatment is performed bya rapid thermal anneal method using one heat source selected from thegroup consisting of a halogen lamp, a metal halide lamp, a xenon arclamp, and a carbon arc lamp.
 4. A method of manufacturing asemiconductor device according to claim 1, wherein the metal element isat least one selected from the group consisting of Fe, Ni, Co, Ru, Rh,Pd, Os, Ir, Pt, Cu, and Au.
 5. A method of manufacturing a semiconductordevice according to claim 1, wherein the noble gas element is at leastone selected from the group consisting of helium, neon, argon, krypton,and xenon.
 6. A method of manufacturing a semiconductor devicecomprising the steps of: adding a metal element to a semiconductor filmhaving an amorphous structure; crystallizing the semiconductor film by afirst heat treatment to form a crystalline semiconductor film;irradiating the crystalline semiconductor film with laser light toimprove crystallinity; forming an impurity region to which a noble gaselement is selectively added in the crystalline semiconductor film; andsegregating the metal element in the impurity region containing thenoble gas element by a second heat treatment.
 7. A method ofmanufacturing a semiconductor device according to claim 6, wherein thefirst heat treatment is performed by a rapid thermal anneal method usingone heat source selected from the group consisting of a halogen lamp, ametal halide lamp, a xenon arc lamp, and a carbon arc lamp.
 8. A methodof manufacturing a semiconductor device according to claim 6, whereinthe laser light is emitted using one selected from the group consistingof an excimer laser, a YAG laser, a YVO₄ laser, or a YLF laser.
 9. Amethod of manufacturing a semiconductor device according to claim 6,wherein the second heat treatment is performed by a rapid thermal annealmethod using one heat source selected from the group consisting of ahalogen lamp, a metal halide lamp, a xenon arc lamp, and a carbon arclamp.
 10. A method of manufacturing a semiconductor device according toclaim 6, wherein the metal element is at least one selected from thegroup consisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au. 11.A method of manufacturing a semiconductor device according to claim 6,wherein the noble gas element is at least one selected from the groupconsisting of helium, neon, argon, krypton, and xenon.
 12. A method ofmanufacturing a semiconductor device comprising the steps of: adding ametal element to a semiconductor film having an amorphous structure;crystallizing the semiconductor film by a first heat treatment to form acrystalline semiconductor film; forming an impurity region to which anoble gas element is selectively added in the crystalline semiconductorfilm; and segregating the metal element in the impurity regioncontaining the noble gas element by a second heat treatment; andremoving the impurity region containing the noble gas element byetching.
 13. A method of manufacturing a semiconductor device accordingto claim 12, wherein the first heat treatment is performed by a rapidthermal anneal method using one heat source selected from the groupconsisting of a halogen lamp, a metal halide lamp, a xenon arc lamp, anda carbon arc lamp.
 14. A method of manufacturing a semiconductor deviceaccording to claim 12, wherein the second heat treatment is performed bya rapid thermal anneal method using one heat source selected from thegroup consisting of a halogen lamp, a metal halide lamp, a xenon arclamp, and a carbon arc lamp.
 15. A method of manufacturing asemiconductor device according to claim 12, wherein the metal element isat least one selected from the group consisting of Fe, Ni, Co, Ru, Rh,Pd, Os, Ir, Pt, Cu, and Au.
 16. A method of manufacturing asemiconductor device according to claim 12, wherein the noble gaselement is at least one selected from the group consisting of helium,neon, argon, krypton, and xenon.
 17. A method of manufacturing asemiconductor device comprising the steps of: adding a metal element toa semiconductor film having an amorphous structure; crystallizing thesemiconductor film by a first heat treatment to form a crystallinesemiconductor film; irradiating the crystalline semiconductor film withlaser light to improve crystallinity; forming an impurity region towhich a noble gas element is selectively added in the crystallinesemiconductor film; and segregating the metal element in the impurityregion containing the noble gas element by a second heat treatment; andremoving the impurity region containing the noble gas element byetching.
 18. A method of manufacturing a semiconductor device accordingto claim 17, wherein the first heat treatment is performed by a rapidthermal anneal method using one heat source selected from the groupconsisting of a halogen lamp, a metal halide lamp, a xenon arc lamp, anda carbon arc lamp.
 19. A method of manufacturing a semiconductor deviceaccording to claim 17, wherein the laser light is emitted using oneselected from the group consisting of an excimer laser, a YAG laser, aYVO₄ laser, or a YLF laser.
 20. A method of manufacturing asemiconductor device according to claim 17, wherein the second heattreatment is performed by a rapid thermal anneal method using one heatsource selected from the group consisting of a halogen lamp, a metalhalide lamp, a xenon arc lamp, and a carbon arc lamp.
 21. A method ofmanufacturing a semiconductor device according to claim 17, wherein themetal element is at least one selected from the group consisting of Fe,Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au.
 22. A method ofmanufacturing a semiconductor device according to claim 17, wherein thenoble gas element is at least one selected from the group consisting ofhelium, neon, argon, krypton, and xenon.
 23. A method of manufacturing asemiconductor device comprising the steps of: adding a metal element toa semiconductor film having an amorphous structure; crystallizing thesemiconductor film by a first heat treatment to form a crystallinesemiconductor film; forming a mask insulating film having an opening onthe crystalline semiconductor film; forming an impurity region to whichan ion of a noble gas element accelerated by an electric field is addedin the crystalline semiconductor film through the opening; andsegregating the metal element in the impurity region containing the ionof the noble gas element by a second heat treatment.
 24. A method ofmanufacturing a semiconductor device according to claim 23, wherein thefirst heat treatment is performed by a rapid thermal anneal method usingone heat source selected from the group consisting of a halogen lamp, ametal halide lamp, a xenon arc lamp, and a carbon arc lamp.
 25. A methodof manufacturing a semiconductor device according to claim 23, whereinthe second heat treatment is performed by a rapid thermal anneal methodusing one heat source selected from the group consisting of a halogenlamp, a metal halide lamp, a xenon arc lamp, and a carbon arc lamp. 26.A method of manufacturing a semiconductor device according to claim 23,wherein the metal element is at least one selected from the groupconsisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au.
 27. Amethod of manufacturing a semiconductor device according to claim 23,wherein the noble gas element is at least one selected from the groupconsisting of helium, neon, argon, krypton, and xenon.
 28. A method ofmanufacturing a semiconductor device comprising the steps of: adding ametal element to a semiconductor film having an amorphous structure;crystallizing the semiconductor film by a first heat treatment to form acrystalline semiconductor film; irradiating the crystallinesemiconductor film with laser light to improve crystallinity; forming amask insulating film having an opening on the crystalline semiconductorfilm; forming an impurity region to which an ion of a noble gas elementaccelerated by an electric field is added in the crystallinesemiconductor film through the opening; and segregating the metalelement in the impurity region containing the ion of the noble gaselement by a second heat treatment.
 29. A method of manufacturing asemiconductor device according to claim 28, wherein the first heattreatment is performed by a rapid thermal anneal method using one heatsource selected from the group consisting of a halogen lamp, a metalhalide lamp, a xenon arc lamp, and a carbon arc lamp.
 30. A method ofmanufacturing a semiconductor device according to claim 28, wherein thelaser light is emitted using one selected from the group consisting ofan excimer laser, a YAG laser, a YVO₄ laser, or a YLF laser.
 31. Amethod of manufacturing a semiconductor device according to claim 28,wherein the second heat treatment is performed by a rapid thermal annealmethod using one heat source selected from the group consisting of ahalogen lamp, a metal halide lamp, a xenon arc lamp, and a carbon arclamp.
 32. A method of manufacturing a semiconductor device according toclaim 28, wherein the metal element is at least one selected from thegroup consisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au. 33.A method of manufacturing a semiconductor device according to claim 28,wherein the noble gas element is at least one selected from the groupconsisting of helium, neon, argon, krypton, and xenon.
 34. A method ofmanufacturing a semiconductor device comprising the steps of: adding ametal element to a semiconductor film having an amorphous structure;crystallizing the semiconductor film by a first heat treatment to form acrystalline semiconductor film; forming a mask insulating film having anopening on the crystalline semiconductor film; forming an impurityregion to which an ion of a noble gas element accelerated by an electricfield is added in the crystalline semiconductor film through theopening; segregating the metal element in the impurity region containingthe ion of the noble gas element by a second heat treatment; andremoving the impurity region containing the ion of the noble gas elementby etching.
 35. A method of manufacturing a semiconductor deviceaccording to claim 34, wherein the first heat treatment is performed bya rapid thermal anneal method using one heat source selected from thegroup consisting of a halogen lamp, a metal halide lamp, a xenon arclamp, and a carbon arc lamp.
 36. A method of manufacturing asemiconductor device according to claim 34, wherein the laser light isemitted using one selected from the group consisting of an excimerlaser, a YAG laser, a YVO₄ laser, or a YLF laser.
 37. A method ofmanufacturing a semiconductor device according to claim 34, wherein thesecond heat treatment is performed by a rapid thermal anneal methodusing one heat source selected from the group consisting of a halogenlamp, a metal halide lamp, a xenon arc lamp, and a carbon arc lamp. 38.A method of manufacturing a semiconductor device according to claim 34,wherein the metal element is at least one selected from the groupconsisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au.
 39. Amethod of manufacturing a semiconductor device comprising the steps of:adding a metal element to a semiconductor film having an amorphousstructure; crystallizing the semiconductor film by a first heattreatment to form a crystalline semiconductor film; irradiating thecrystalline semiconductor film with laser light to improvecrystallinity; forming a mask insulating film having an opening on thecrystalline semiconductor film; forming an impurity region to which anion of a noble gas element accelerated by an electric field is added inthe crystalline semiconductor film through the opening; segregating themetal element in the impurity region containing the ion of the noble gaselement by a second heat treatment; and removing the impurity regioncontaining the ion of the noble gas element by etching.
 40. A method ofmanufacturing a semiconductor device according to claim 39, wherein thefirst heat treatment is performed by a rapid thermal anneal method usingone heat source selected from the group consisting of a halogen lamp, ametal halide lamp, a xenon arc lamp, and a carbon arc lamp.
 41. A methodof manufacturing a semiconductor device according to claim 39, whereinthe laser light is emitted using one selected from the group consistingof an excimer laser, a YAG laser, a YVO₄ laser, or a YLF laser.
 42. Amethod of manufacturing a semiconductor device according to claim 39,wherein the second heat treatment is performed by a rapid thermal annealmethod using one heat source selected from the group consisting of ahalogen lamp, a metal halide lamp, a xenon arc lamp, and a carbon arclamp.
 43. A method of manufacturing a semiconductor device according toclaim 39, wherein the metal element is at least one selected from thegroup consisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au. 44.A method of manufacturing a semiconductor device according to claim 39,wherein the noble gas element is at least one selected from the groupconsisting of helium, neon, argon, krypton, and xenon.